4. How transduction was
• Studied in Salmonella typhimurium
• Plated two auxotrophic strains (LA-2 and LA-22)
individually on minimal medium, no cells grew.
• Plated a mixture of the two auxotrophic strains on
minimal medium, cells grew into colonies.
• Thus, genetic exchange was taking place between the
two cell types.
Definition - Unlike transformation in which the
naked DNA is transferred in transduction DNA is
carried by a bacteriophage.
In transduction, DNA is transferred from cell to cell
through the agency of viruses
NOTE :- All phages can be transducer and not all
bacteria are transducible
8. Transduction has been found to occur in a variety
of prokaryotes, including certain species of the
Bacteria: Desulfovibrio, Escherichia,
Pseudomonas, Rhodococcus, Rhodobacter,
Salmonella, Staphylococcus, and Xanthobacter, as
well as Methanobacterium thermoautotrophicum.
Mechanism of Transduction
• Firstly Descovered in 1915 by Fredrick Twort
and two years later by Felix d’Herelle.
• Means bacteria eater.
• A virus that infects certain type of bacteria and
replicates within them
10. Types of bacterio-phage
Virulent: capable of causing infection and
eventually destruction and death of the bacterial
cell. These follow the lytic cycle. e.g. T4 host
Temperate: does not cause destruptic infection
instead phage DNA is incorporated into
bacterium DNA and is replicated with it and after
some cycle become virulent cause lysis.
• e.g. lambda phage. 10
• There are two types of transduction:
– Generalized transduction: A DNA
fragment is transferred from one bacterium
to another by a lytic bacteriophage that is
now carrying donor bacterial DNA due to an
error in maturation during the lytic life cycle.
13. Generalised Transduction
1. A lytic bacteriophage adsorbs to
a susceptible bacterium.
2. The bacteriophage genome
enters the bacterium. The genome
directs the bacterium's metabolic
machinery to manufacture
bacteriophage components and
3. Occasionally, a bacteriophage head
or capsid assembles around a fragment
of donor bacterium's nucleoid instead
of a phage genome by mistake.
steps in Generalised Transduction (cont’d)
4. The bacteriophages are released.
15. steps in Generalised Transduction (cont’d)
5. The bacteriophage carrying the
donor bacterium's DNA adsorbs to a
6. The bacteriophage inserts the donor
bacterium's DNA it is carrying into the
recipient bacterium .
steps in Generalised Transduction (contd)
7. The donor bacterium's DNA is exchanged for some of
the recipient's DNA.
17. • Specialized transduction:
• A DNA fragment is transferred from one
bacterium to another by a temperate
bacteriophage that is now carrying donor
bacterial DNA due to an error in spontaneous
induction during the lysogenic life cycle.
• In specialized transduction the phage inserts
its genome at the specific site.
18. Specialised Transduction
1. A temperate bacteriophage adsorbs
to a susceptible bacterium and injects
its genome .
2. The bacteriophage inserts its genome
into the bacterium's nucleoid to become
19. Steps in Specialised Transduction (cont’d)
3. Occasionally during spontaneous
induction, a small piece of the donor
bacterium's DNA is picked up as part of
the phage's genome in place of some of
the phage DNA which remains in the
4. As the bacteriophage replicates, the
segment of bacterial DNA replicates as
part of the phage's genome. Every
phage now carries that segment of
20. Steps in Specialised Transduction (cont’d)
5. The bacteriophage adsorbs to a
recipient bacterium and injects its
6. The bacteriophage genome carrying
the donor bacterial DNA inserts into the
recipient bacterium's nucleoid.
21. Significance of transduction
• It transfers genetic material from one bacterial cell to
another and alter the genetic characteristics.
• For example: In specialised transduction the gal gene, a cell
lacking ability to metabolize galactose could aquire the
• It shows the evolutionary relationship between the prophage
and host bacterial cell.
• Prophage can exist in a cell for a long period suggests a
similar possible mechanism for the viral origin of cancer.
• It provides a way to study the gene linkage.